What are the major histological features of the small intestinal mucosa?

• A. Cortex and paracortex; B and T cells.
• B. Alveolar space; type I and II pneumocytes.
• C. Portal triad.
• D. Villi and crypts; enterocytes with microvilli; goblet cells; underlying muscularis mucosae.

Answer: (D)

The mucosa of the small intestine is specialized for absorption, and its major histological features reflect that function: finger-like villi that project into the lumen to greatly increase surface area; deep tubular glands called crypts of Lieberkühn at the base of the mucosa where new cells are produced; the epithelial lining consists of simple columnar enterocytes with an apical brush border formed by dense microvilli, maximizing nutrient absorption and housing digestive enzymes; scattered goblet cells that secrete mucus to lubricate and protect the lining; and a thin muscularis mucosae lying beneath the mucosa that helps local movement and folding of the mucosa. Beneath this layer lies the lamina propria with capillaries and lymphatics to transport absorbed nutrients. These features—villi and crypts with enterocytes bearing microvilli and goblet cells, plus the underlying muscularis mucosae—define the small intestinal mucosa.